Brian Littrell, Nick Carter, Howie Dorough, A.J. McLean and yes, even Kevin Richardson, reunited for the first time in six years to perform a selection of their biggest hits during a Friday Good Morning America concert in New York City's Central Park.

Currently working on their fifth studio album, which they'll release with the help of original member Richardson, 40 -- who left his band mates Littrell, 37, Carter, 32, Dorough, 38, and McLean, 34 in 2006 -- BSB belted out "Larger Than Life," "Everybody (Backstreet's Back), "Incomplete" and "I Want It That Way" for a massive outdoor audience.

Mike Prior/RedfernsBackstreet Boys in London in 1996.

Following the group's opening number, "Incomplete," GMA anchor Josh Elliott offered a quick song dedication. "Robin, that one was for you," Elliott said, referring to beloved GMA mainstay Robin Roberts, whose mother, Lucimarian, passed away Thursday -- just days before Roberts is scheduled to undergo a bone marrow transplant using a donation from her sister Sally-Ann.

"We definitely have some of the best fans in the world, that's for sure," Carter told anchor Lara Spencer. "It's like we never stopped -- and now we've got Kev back, so now Backstreet's back," added McLean.